Composite woods products may be described as falling into five classes, each characterized by the treatment of the wood within the product: plywood, oriented strandboard, particleboard, hardboard, and fiberboard. For each class of composite wood, the configuration of the wood contributes to that product's physical properties and typical application. In addition, the adhesive, the density of the wood, and additives such as resin or fire retardants, may change the characteristics of the product.
Most composite woods are made using a thermosetting or heat curing adhesive to bind or hold the cellulose wood fibers together during the process of manufacturing. Commonly used composite wood adhesives or resin binders are formaldehyde, urea-formaldehyde, melamine-formaldehyde, and isocyanate. Phenol-formaldehyde resins are typically used for manufacturing products that require some degree of exterior exposure durability. Urea-formaldehyde resins are typically used in manufacturing products where dimensional uniformity and surface smoothness are of more concern than exterior durability (e.g., particleboard). Melamine-formaldehyde is an expensive resin used in decorative laminates or paper treatment. Isocyanates, such as di-phenylmethane di-isocyanate (or MDI) are also used in the manufacture of composite wood products. Natural adhesives, such as tannins, can be modified and reacted with formaldehyde to produce resins, as well. The curing characteristics of the resin, such as the cure temperature and time, are also additional factors in the choice of resin. Urea- and phenol formaldehyde resins are most widely used in manufacturing composite wood products.
These resins are expensive and may cause environmental and health problems. Oil shortages contribute to price increases. Formaldehyde is an irritant, a suspected carcinogen, and the resin base may release volatile organic compounds. (Toxicological Profile, ATSDR, DHHS-PHS 1999). In the composite wood industry, flour is often used as an extender for these expensive adhesives. Extenders reduce the cost of the resin and the concentration of any deleterious components. Extenders may contribute to prepress tack and have some adhesive action, but the resin solids are the ultimate moisture resistant binder.
Flour extenders known in the field include soy bean protein, casein, starch, oil cakes, corn flour, corn gluten protein, seed gums, and primarily wheat flour. In some cases, wheat and other flours or materials may be mixed. The combination of gluten or protein and starch in wheat flour appears to aid in the adhesiveness or tack of the final mixture, making it one of the most widely used extenders. Yet wheat flour, although cheaper than resin, is still relatively expensive compared to many other natural alternatives. Wheat flour is also somewhat unpredictable or variable. The proteins in wheat flour can cause stringing and lumping of the adhesive mixture, and accumulation or build up of glue on spray tips or other equipment, necessitating frequent cleaning. Thus, some have sought natural alternatives, such as fiber byproducts mixed with starch, but with limited commercial acceptance.
Accordingly, an object of the present invention is to provide an adhesive, adhesive extenders and mixture thereof for use in composite wood products satisfactory to the performance and manufacturing needs, as well as a method for the production and use of such an adhesive or adhesive extender in the manufacture of composite wood products.
It is an object of the present invention to accomplish the foregoing objective in a simple and cost effective manner.
Additional objects and advantages of embodiments of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be obtained by means of instrumentalities in combinations particularly pointed out in the appended claims.